In many industrial applications a pattern is created in a layer at the surface of a fabricated object. For example, electronic devices such as semiconductor chips are formed from multilevel structures having layers of patterned semiconducting materials, metals, and dielectric materials. In microelectronics the various intricate patterns necessary to form, for example, the various doped regions of silicon on a chip or their interconnections or the various interconnections on a package are delineated by lithographic techniques. Lithography relies on energy sensitive materials generally called resists. An energy sensitive material is disposed on a surface. The layer of energy sensitive material is exposed to a pattern of energy which alters the properties of the layer in the exposed regions so that either the exposed or unexposed regions can be subsequently removed to form a pattern in the energy sensitive layer. In positive acting resists the exposed regions generally become more soluble than the unexposed regions whereas in negative acting resists the exposed regions become more insoluble. The more soluble regions are generally removed with a suitable solvent during the development step. In both the positive and negative resists, after development, a pattern has been generated in the resist or energy sensitive layer. This pattern can then be transferred down to underlying layers by various etching mechanisms.
Where the pattern of energy results in generation of electrical charge or carries an electrical charge such as in electron beam lithography, electrical charge can in turn accumulate at the energy sensitive layer or in the underlying layers which can result in distortion of the pattern being created in the energy sensitive layer. Such distortions create huge image placement variations and errors. This occurs when a dielectric energy sensitive material such as a resist is exposed to a charged beam such as an electron beam or an ion beam. The dielectric energy sensitive layer accumulates charge from the beam. The accumulated charge introduces electric fields which after reaching a sufficient magnitude distorts the beam and results in a misplacement of the beam on the energy sensitive material. This creates errors in the pattern being formed in the layer.
In addition, charging is a problem in metrology. Metrology of device wafers or masks is generally done by Scanning Electron Microscopy (SEM). As IC device features continue to decrease into the sub 0.5 um region, SEM is becoming a commonplace technique for the inspection and dimensional measurements (metrology) of these circuits. Charging of the sample during SEM makes accurate metrology difficult. As an electric field builds up on the sample, the electron beam can be deflected. Even a very small beam deflection around a feature can move the beam one or two pixel points. If this occurs, substantial error is introduced into the measurement of the critical dimensions. One method to somewhat alleviate the charging problem is to do SEM at low accelerating voltages. However, at such voltages the resolution of the measurements is sacrificed.
Previously we disclosed the use of a conducting polymer applied to the surface of the imaging resist or on the surface of a device wafer or mask being inspected to eliminate charging (U.S. Pat. Nos. 5,198,153, 5,200,112, 5,202,061 and 5,370,825, the teaching of which is incorporated herein by reference). In particular, a water soluble polyaniline was found to be easily applied on to the surface of a resist or mask or device wafer to eliminate charging during electron beam exposure or during SEM metrology. FIG. 1 depicts a pattern that was written with electron beam with no conducting polymer layer (a) and a pattern written with a thin coating of the polyaniline (1000-2000 A) (b). Significant image distortion is observed in (a) whereas a more well defined feature is observed (b). In addition, FIG. 2 depicts SEM metrology of a mask that is uncoated (a) and metrology of a mask that is coated with the polyaniline (b). As can be seen, no charging is observed in(b).
Although this process of applying a secondary conducting coating works well in eliminating charging, it is not an ideal solution. For SEM metrology, the coating can alter the critical dimensions being measured. The coating can introduce defects during its application and during its removal. A more desirable process would be to have an inherently conducting or dissipative resist system. This would eliminate the need for secondary dissipative coatings.
Herein, an admixture of an energy sensitive layer and a layer of an electrically conducting material is disclosed thereby forming an inherently conducting resist. The conducting resist allows direct imaging with a charged beam and allows high resolution SEM metrology.
Electrically conductive organic polymers are a class of electronic materials that combine the electrical properties of metals with the processability and mechanical properties characteristic of conventional polymers. Examples of such polymers include polyparaphenylene vinylenes, polyparaphenylenes, polyanilines, polythiophenes, polyazines, polyfuranes, polypyrroles, polyselenophenes, poly-p-phenylene sulfides, polythianapthenes, polyacetylenes formed from soluble precursors, combinations thereof and blends thereof with other polymers and copolymers of the monomers thereof.
These polymers are conjugated systems which are made electrically conducting by doping. The non-doped or non-conducting form of the polymer is referred to herein as the precursor to the electrically conducting polymer. The doped or conducting form of the polymer is referred to herein as the conducting polymer. Herein admixtures of electrically conducting polymers with energy sensitive materials are disclosed.